Systems for aggregating and processing of biogas to biomethane

ABSTRACT

A biogas collection and purification system that includes a plurality of sources of biogas and a network of conduits configured to convey the biogas from the sources to a central processing facility for processing the biogas into methane. The central processing facility removes impurities to convert biogas to biomethane and may include an H 2 S removal stage; an activated carbon scrubber; a gas drier; and a carbon dioxide removal stage. The facility also has a biomethane gas compressor configured to deliver the biomethane for use in power plants, for CNG production. Ancillaries to the system include fuel cells for direct electricity generation from biogas/biomethane.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure claims priority to and is a non-provisionalconversion of U.S. Provisional Patent Application No. 62/802,502, filedFeb. 7, 2019, all of which is incorporated herein by reference in itsentirety for all purposes.

FIELD OF THE INVENTION

The technology relates to the field of biogas conversion to biomethanefor energy generation, and more particularly relates to the collectionof biogas from a plurality of sources generating biogas fromdecomposition of organic waste, at a range of geographic locations, androuting the collected biogas to location(s) for processing intobiomethane and/or generation of electricity.

DESCRIPTION OF THE RELATED ART

Electricity is a necessary power source in a modern technology-basedeconomy, and also in those economies that are developing into moderneconomies, which have exhibited a great demand for more electric poweras standards of living improve. Initially, the basic source forelectricity generation was combustion of coal (carbon), or oil(hydrocarbons), both of which are often called “fossil fuels.” Both coaland hydrocarbon oils generate carbon dioxide as a combustion byproduct,and carbon dioxide is a greenhouse gas that contributes to thephenomenon of global warming, or climate change.

Electricity has also been generated as hydro-electric power by turbinesdriven by flow of water, typically at dams when water is releasedthrough sluice gates to drive the turbines. More recently, there hasbeen an upsurge in generation of electricity using solar power as thecost of solar cell panels have begun to decline thereby reducing thecost per KW-hr of electricity generated. In addition, the use of windpower turbines, especially in Texas and California, has causedelectricity from wind power to become a significant part of the supplyto the power grid. Solar and Wind both suffer the disadvantage of beingintermittent (not schedulable) sources of electricity.

There also continues to be growing interest in both small as well aslarge scale generation of biogas (typically 60% methane) that can bepurified into a “renewable natural gas” or RNG, a more purifiedcombustible gas (generally at least 95% pure methane) from waste.Ordinarily, this biogas is a natural product of the decomposition oforganic waste material, most often though an anaerobic process, and isreleased into the atmosphere. In the atmosphere, it is believed thatbiogas, especially the methane component, is a “greenhouse gas” thatcontributes to the phenomenon of global warming, or climate change. Onthe other hand, if the biogas could be captured and treated to generateelectricity or processed into RNG, this methane gas could be used togenerate power in methane-burning power plants or fuel compressednatural gas vehicles with the previously vented methane being destroyedin the process thus eliminating its greenhouse gas effect. Moreover, thesubstitution of bio-derived gas for transportation fuels, such ascompressed natural gas (“CNG”) presents a further opportunity to backout fossil fuel combustion and thereby reduce greenhouse gas emissions.

Methane has a lower carbon to hydrogen ratio than coal or hydrocarbonoils. Thus, methane produces less carbon dioxide upon combustion. As aresult the net effect of this capture of methane, and subsequentcombustion to produce electricity, is to “back out” other fuel sourcesthat would have been combusted in the power plants, such as coal orhydrocarbon oils. This is highly beneficial since the combustion ofmethane produces less carbon dioxide per KW-hr of electricity or lesscarbon dioxide per brake horsepower-hour of a vehicle engine, than thecombustion of other hydrocarbon fuels because of its lower carbon tohydrogen ratio. Thus, the removal of the biogas preventing release intothe atmosphere, and the combustion of methane from the biogas providesenergy has a two-fold benefit in reducing greenhouse gas emissions:reduction of biogas into the atmosphere, and less combustion of carbondioxide emissions in electricity generation by “backing out” coal orother hydrocarbons that have a higher carbon to hydrogen ratio.Moreover, organic waste generation and decomposition to produce biogasare continuously ongoing processes, so that biogas is, in that sense, apotentially continuously “renewable” energy supply.

SUMMARY

The technology presented herein provides access to remote biogas sources(“digesters”) that are geographically widely distributed, predicts(based on instrumentation) the availability and quality of biogas fromthese remote sources typically 24 hours in advance, conditions andprepares the biogas to safely aggregate the biogas via a network ofconduits and conveys the biogas to biogas consuming devises(“generators”) and/or to a single treatment facility where it isconverted to RNG or biomethane and controlledly compressed into anatural gas pipeline for subsequent use as combustion fuel, compressionto CNG or LNG (liquified natural gas) for vehicle fuel use, or use infuel cells to create electricity directly. Electricity generated at thetreatment facility, or at the remote biogas sources, can be useddirectly or indirectly (via a contract rather than physical delivery ofelectrons) to provide a renewable source of electrical energy forplug-in battery-powered powered electric vehicles (PEVs), therebyproviding the desirable goal of converting biogas to cleantransportation energy.

In an exemplary embodiment there is provided a biogas production,conditioning, collection, electrical generation, purification anddelivery system. The system aggregates biogas from a plurality of remotesources and treats the biogas to produce electricity and/or biomethane.The system comprises: a network of conduits configured to convey biogasfrom the plurality of remote sources of the biogas based on a monitoredor automatically detected availability and quality of biogas at eachrespective remote source. A biogas compressor at each of the remotelocations is controlled by a central controller that utilizes data thatincludes biogas availability and quality data. The central controller isconfigured to instruct the remote biogas compressor(s) to supplycompressed biogas to several potential processes, as well as to acentral biogas processing facility, depending upon input data. Thus, thebiogas may be compressed to a fuel cell or to an internal combustionengine powered generator for direct conversion of the biogas toelectricity to power at least some of the equipment at the remote sourceor at the centralized facility, or the electricity can be transmitted toa charging station for PEVs to charge vehicle batteries. Compressedbiogas can also be supplied to a biogas header that conveys the biogasto the central processing facility. Here, the received biogas from manyremote sources in the network of linked-together plurality of remotesources is treated and processed from biogas into biomethane and/or alsoconverted to electricity pre (as biogas fuel) or post upgrading (asbiomethane fuel). The central processing facility has an inputcompressor that is controlled by the central controller that operatesbased on data including the data from the remote sources about theavailability of biogas at the sources. The central treatment facilityincludes several biogas treatment operations, including but not limitedto a biogas hydrogen sulfide removal stage; an activated carbon scrubber(which may be downstream from the hydrogen sulfide removal stage); acarbon dioxide removal stage (which may be) downstream from the hydrogensulfide removal stage for purifying the biogas into biomethane byremoval of carbon dioxide. And the central processing facility also hasa biomethane gas compressor for compressing the produced biomethane,also under control of the central controller. Thus, the biomethane maybe charged to a generator such as a fuel cell for direct conversion ofthe biomethane to electricity to power at least some of the equipment atthe treatment facility, or the electricity and/or its environmentalattributes can be transmitted (e.g. directly or virtually via acontract) to a charging station for PEVs to charge vehicle batteries.The biomethane can also be charged to a system for compression torenewable compressed natural gas (R-CNG) for use as a vehicle fuel. Or,the biomethane can be compressed to a natural gas pipeline, as explainedin more detail here below. The decision (and control) of the biomethanedisposition to the natural gas pipeline or to CNG or to fuel cells tocreate electricity for PEVs is based on several control variablesincluding biogas availability, projected biogas availability, quality,quantity, moisture content, presence or absence of contaminants,hydrogen sulfide levels, oxygen levels, nitrogen levels, historicalproduction rates, projected generator or upgrading plant demand rates,upcoming system maintenance inputs, digester status, digester feedstockavailably, ambient temperature and digester efficiency factors, currentbiogas storage levels and remaining biogas storage levels.

The sources of biogas may include organic animal waste anaerobicdigesters, such as for example dairy farm animal waste, and/or capturedbiogas from waste water treatment plant digesters, special purposeorganic waste or mixed substrate digesters, landfills and orcombinations of these sources.

The plurality of sources of biogas of the exemplary embodiment mayinclude biogas sources located remote from each other, and the networkof conduits enable fluid communication between the remote sources and acentral biogas header that is the portion of the network carrying biogasto be received at the central processing facility.

A consideration to bear in mind is that to safely and efficiently conveybiogas in a conduit it is (likely) necessary to “condition” the biogasto remove most of its hydrogen sulfide and water prior and in some casesits carbon dioxide prior to its insertion into the gathering/collectionline. This conditioning of the biogas will occur at or close to thedigester source and prior to compression into the gathering orcollection line. If the biogas is utilized by an internal combustionengine or fuel cell generator directly from the gathering line it mayneed further polishing to remove all traces of contaminants such ashydrogen sulfide or siloxanes.

The biogas hydrogen sulfide removal stage of the central processingfacility of the exemplary embodiment may include a sodium hydroxide gasscrubber or an iron sponge column.

At least some of the sources of biogas of the exemplary embodiment mayinclude a gas quality sensor (measuring and logging for example thepercent of methane, oxygen, carbon dioxide, moisture, hydrogen sulfide)and a gas quantity flow meter. The quantity and quality of the energyexported form each digester feeds the control system and also theaccounting system for allocation of payments back to the owner orlandlord hosting the digester. A hydrogen sulfide sensor located toconfirm quality is acceptable and/or to detect release of hydrogensulfide into a surrounding vicinity of the at least some of the sourcesand activate a central controller to shut a valve to cut off flow ofbiogas, as necessary, to eliminate or minimize leakage upon detection ofhydrogen sulfide gas. It is also important to detect hydrogen sulfidefor other reasons: hydrogen sulfide poisons upgrader membranes orpressure swing absorbents, poisons fuel cells, and damages internalcombustion engines. So, the sensor should supply input to the controlsystem to confirm acceptable quality. [Currently in California thecollection line, by permit and safety considerations, cannot have >10ppm H2S (sometimes up to 100 ppm H2S is OK, typical biogas is 2000-5000ppm H2S.

The remote sources of biogas may each include a flow sensor configuredto detect a flow of biogas from the source. The flow sensor data istransmitted to a central controller that controls a valve, such as athree-way valve, to recycle a portion of the flow back to the respectivesource of biogas. The remote sources (digesters) may include a gaschromtograph or other form of gas analyzer supplying data to the controlsystem to ensure the quality of the biogas is acceptable for delivery tothe collection system and delivery ads a fed gas to the generatorsand/or to the upgrading plant(s). The remote source may include a flowmeter also providing data to the control system to measure the flowquantity of gas for control purposes and also for accounting of thedigester production of energy and its quality into the system.)

At least one of the plurality of biogas sources of the exemplaryembodiment may include a flexible roof over the waste digester. Theflexible roof expands upward when an amount of generated biogas in thedigester increases and biogas pressure increases under the flexibleroof. The biogas source may have an automatic detection device thatprovides data about the amount of biogas available from the digester,such as but not limited to, a laser deflection measurement apparatus.The apparatus may be positioned and configured to measure a degree ofdeflection of the flexible roof as it moves under biogas pressure. Themeasured laser deflection data is transmitted to the central controllerthat controls a compressor that draws biogas from the digester of therespective biogas source based on the data that includes data aboutbiogas availability. Alternatively, or in addition, biogas availabilitycan also be estimated by periodic human inspection. These inspectionscould be weekly, daily or several times per day depending on theproduction rate and remaining storage capacity of the digester. Thus,from observation, if the roof is “highly deflected upward,” more biogasis available. Conversely, when the roof deflection is lower and/ordeclining, less biogas is available.

The foregoing presents a brief and non-comprehensive summary of someaspects of the technology that is further explained in more detail, herebelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thepresent technology will be more readily appreciated by reference to thefollowing Detailed Description, when taken in conjunction with theaccompanying simplified drawings of exemplary embodiments. The drawings,briefly described here below, are not to scale, are presented for easeof explanation and do not limit the scope of the inventions recited inthe accompanying patent claims.

FIG. 1 is a simplified schematic overview illustration of an exemplaryembodiment of the system for aggregating and processing of biogas toelectrical generation and/or to methane, according to the invention.

FIG. 2 is a simplified schematic illustration of an exemplary embodimentof the processing system converting biogas to methane, according to theinvention.

FIG. 3 is a simplified schematic illustration of an exemplary biogassource that may be a part of the system for aggregating and processingof biogas to methane, according to the invention.

FIG. 4 is an illustrative simplified process flow diagram of anexemplary embodiment of a biogas processing facility at a remote source.

FIG. 5 is an illustrative simplified process flow diagram of anexemplary embodiment of a central facility processing biogas from aplurality of biogas remote sources to biomethane.

DETAILED DESCRIPTION

The following non-limiting detailed descriptions of examples ofembodiments of the invention may refer to appended Figure drawings andare not limited to the drawings, which are merely presented forenhancing explanations of features of the technology. In addition, thedetailed descriptions may refer to particular terms of art, some ofwhich are defined herein, as appropriate and necessary for clarity.

In the specification and claims, the term “remote,” as it pertains tothe geographic location of biogas sources that are linked by the networkof conduits to a portion of the network (a common biogas header pipe)that conveys and feeds biogas to the central treatment/processingfacility, means that the biogas sources are geographically distant fromeach other (i.e. not located on the same farm, or waste disposal site,for example). Absent the network of conduits, the biogas supply fromthese sources would have been processed separately at each of the biogassources, if at all.

A “biogas source,” as the term is used in the specification and claims,means a source of biogas such as, but not limited to, an organic wastedigester that digests animal waste (e.g. manure from a dairy or a wastedisposal site) or a landfill, for example, and may include severaldigesters/landfills at the same geographic location that are linkedtogether and may be counted as a single remote biogas source.

A remote location may include a biogas conditioning plant that not onlyremoves hydrogen sulfide and water but also removes carbon dioxide thusreducing the quantity of gas that is needed to be collected andtransported to the generators and/or to the centralized upgrading plant.This could be a membrane-based biogas conditioning package thatselectively separates methane form H20, H2S and CO2. In an exemplaryembodiment, the centralized upgrading plant could receive biomethane (asopposed to biogas) and thus its primary purpose would be, under controlof the central processor to accept this feed gas, remove any residualcontaminants in order to meet pertinent applicable utilityspecifications, and then compressing and injecting the purifiedbiomethane into the pipeline.

A networked collection system may also include a portion of the systemwhere the biogas or biomethane is conveyed from the remote sourcelocation to the centralized location, or generators, via tank cars. Thetransported biogas may be off loaded at the centralized treatment plantfor purification, quality control and delivery into the pipeline. Thecontrol and reporting of this “virtual” pipeline would also provide datato the central controller so that the entire system is coordinated andcontrolled.

In general, the processing of biogas to biomethane at each locationwhere biogas is produced means that equipment and labor has to beexpended at each location. Often, this is not economically feasible.According to exemplary embodiments of the invention, biogas from ageographically widely spread out plurality of biogas sources can beaccumulated in a network of conduits (pipelines), often linked into acommon header pipe, and carried in these conduits to a central gastreatment/processing facility. In addition, in order to deliver theproduced biomethane (RNG) it is necessary to bring it to a centralizedlocation where the local gas utility is ready willing and able toreceive the gas into their natural gas distribution or transmissionsystem for delivery downstream to customers. This minimizes the outlayof capital in equipment but increases the cost of the conduits. However,advantageously, these conduits may be of inexpensive polymer materialsthat are impervious to attack by chemicals found in biogas, such aswater and hydrogen sulfide, which has a highly offensive odor (“rottenegg stench”) and is readily detected. However, the collection, oraggregation, of the biogas from far-ranging farms, landfills and othersources and processing of the aggregated volume of biogas to biomethanepresents several challenges that must be met to produce methane that isof a purity acceptable for combustion in power plants, and for use inproducing CNG, while maintaining standards of safety.

In addition to the challenges of biogas aggregation, transport andprocessing, there is also the issue of distribution of the producedbiomethane into natural gas pipelines. In general, pipelines have asystem of requiring a gas supplier to contract in advance (by about 24hours) the volume of approved quality methane it will be able to supplyto the pipeline. Failure to meet the contracted supply results inpenalties. Accordingly, there must be an accurate determination made inadvance (about (or typically??) 24 to 36 hours in advance) of the amountof biogas that will be available to convert to biomethane for chargingto a natural gas pipeline, and the remote sources that will supply thisbiogas. In addition, the biogas supply to the central treatment facilitymust be controlled. This presents significant challenges. While naturalgas produced from a geological formation has relatively predictablerates of production or can be turned off an don as needed as it isstored in an existing geological formation, in a biogas supply system,the volume production of biogas is dependent upon many factors,including weather, ambient temperature, conditions at the wastedigesters, remaining storage capacity, and the like that are not readilyand accurately predictable. In addition, biogas may be routed at theremote source to a generator or fuel cell for direct conversion toelectricity into the grid and/or to a PEV charging station, or tooperate equipment at the remote source. Accordingly, the centralcontroller should take into account the amount of biogas available atthe remote sources (whether from manual data input or from automatedmeasurements), and the potential alternative disposition of the biogasand address the challenge of being able to predict at least 24-36 hoursin advance the availability of biogas to be charged to the treatmentfacility that will produce a predictable supply of biomethane.

The present technology uses data collected at each of the remote sourcesof the system that are able to supply biogas to assess biogasavailability at each source at least about 24-36 hours in advance anduses this data to be able to commit to inject biomethane from thisavailable biogas supply into the natural gas pipeline. The collecteddata is collected automatically or manually estimated at each remotesource and input to the central controller.

As explained in more detail here below, in some examples the wastedigesters have expandable roofs that deflect upward as gas accumulatesunder the roof. The deflection may be measured, by laser, for example,and the gas volume available can be estimated from the deflection. Thisprovides a means for estimation of the total volume of biogas that couldbe continuously processed to biomethane and injected into a pipeline. Ofcourse, other methods than roof deflection measurements may also beused. For example, human observation, or measurement of biogas pressureunder the roof.

Several exemplary embodiments of systems that treat biogas to producebiomethane for natural gas pipeline injection (or other disposition asdescribed herein) are set forth here below. As already pointed out hereabove, some of the biogas can be directly converted to electricity infuel cells. And, as pointed out above, some of the biomethane may beused to make CNG. However, for the sake of simplicity, the explanationsmay focus mainly on biomethane for natural gas pipeline injection. Thereare some common technologies among the provided examples, and somevariations between them as to apparatus. Nonetheless, each has in commonthe detection of the volume of biogas available at the remote sourceseither in real time or periodically. In addition, the connecting networkof conduits has a biogas “hold up” volume that is also available to beprocessed as part of the biomethane that is contracted to be delivered.The technology presented herein provides access to remote biogas sourcesthat are geographically widely distributed, predicts (based oninstrumentation and/or human data input) the availability of biogas fromthese remote sources at least 24-36 hours in advance, safely aggregatesthe biogas via a network of conduits, and conveys the biogas to a singleconversion facility to produce biomethane where it is converted tobiomethane and controlledly compressed into a natural gas pipelineand/or supplied to a CNG facility, and/or used in a fuel cell todirectly make electricity.

In summary, in an exemplary embodiment there is provided a biogascollection, purification and biomethane delivery system. The systemaggregates biogas from a plurality of remote sources, deducts remoteuses such as for generation or other biogas take-off, adds virtualdeliveries and treats the biogas to produce biomethane. The systemcomprises: a network of conduits configured to convey biogas from theplurality of remote sources of the biogas based on a monitored orautomatically detected availability of biogas at each respective remotesource. A biogas compressor at each of the remote locations iscontrolled by a central controller that utilizes data that includesbiogas availability data. The central controller is configured toinstruct the biogas compressor to supply compressed biogas to severalpotential processes, as well as to a central biogas processing facility,depending upon input data. Thus, the biogas may be compressed to a fuelcell for direct conversion of the biogas to electricity to power atleast some of the equipment at the remote source, or the electricity canbe transmitted to a charging station for PEVs to charge vehiclebatteries. Compressed biogas can also be supplied to a biogas headerthat conveys the biogas to the central processing facility. Here, thereceived biogas from many remote sources in the network oflinked-together plurality of remote sources is treated and processedfrom biogas into biomethane. The central processing facility has aninput compressor that is controlled by the central controller thatoperates based on data including the data from the remote sources aboutthe availability of biogas at the sources. The central treatmentfacility includes several biogas treatment operations, including but notlimited to a biogas hydrogen sulfide removal stage; an activated carbonscrubber (which may be downstream from the hydrogen sulfide removalstage); a carbon dioxide removal stage (which may be) downstream fromthe hydrogen sulfide removal stage for purifying the biogas intobiomethane by removal of carbon dioxide. And the central processingfacility also has a biomethane gas compressor for compressing theproduced biomethane, also under control of the central controller. Ifthe biogas to biomethane upgrading is handled at some or each remotelocation then the central treatment plant still remains as the controlhub and RNG product quality station to ensure the RNG meets the utilitygas specifications (e.g. Rule 30 for Sempra and Rule 21 for PG&E) Thus,the biomethane may be charged to a fuel cell for direct conversion ofthe biomethane to electricity to power at least some of the equipment atthe treatment facility, or the electricity can be transmitted to acharging station for PEVs to charge vehicle batteries. The biomethanecan also be charged to a system for compression to CNG. Or, thebiomethane can be compressed to a natural gas pipeline, as explained inmore detail here below. The decision (and control) of the biomethanedisposition to the natural gas pipeline or to CNG or to fuel cells tocreate electricity for PEVs is based on several control variablesincluding biogas availability, projected biogas availability and (usesame language as previously)

In general, in a simplified explanation of an exemplary embodiment, thecentral processing facility has several processing units. The processingunits may be skid-mounted. Among the processing units are a hydrogensulfide removal stage, which may include, but is not limited to, asodium hydroxide scrubber or iron sponge columns. Further, an activatedcarbon scrubber is deployed downstream from the hydrogen sulfide removalstage to remove further residual amounts of hydrogen sulfide and othercontaminants susceptible to activated carbon removal. To remove watervapor, a drier may be located downstream from the activated carbonscrubber. At this stage, the biogas still has significant amounts ofcarbon dioxide. Thus, a carbon dioxide removal stage, which may include,but is not limited to, a membrane separator that separates out thebiomethane from the carbon dioxide, which may be vented. There may be agas chiller downstream from the carbon dioxide removal stage to chillthe biomethane which is at this point high purity combustible methane. Asystem compressor is configured to compress the biomethane at acontrolled rate of compression that is based on data that may includedata received from the instruments measuring biogas accumulation atbiogas remote sources in the network, but that is also based on theamount of gas being metered into the pipeline. The gas hold-up in theconduit network of the system may also be used as part of the controldata for the compressor.

FIG. 1 is a simplified flow diagram depicting an overview of processflows of an example of a system for aggregating and processing of biogasto methane, according to the invention. The illustrated system 100includes a plurality of remote biogas sources 10, 12. 14, 16, 18, and20. The remote biogas source 20 includes, in the example three digesters(but more or fewer are envisaged) are illustrated, as biogas sources 22,24, and 26 that not remote from each other (i.e. they might be on thesame farm if these are animal waste digesters) but that are remote as agroup from the other illustrated biogas sources 10, 12, 14, 16, and 18.Thus, remote biogas source 20 that includes biogas sources 22, 24 and 26is a remote biogas source, as that term is used herein. The remotebiogas sources each deliver biogas into a network of gas aggregationconduits. In this example, for instance, remote biogas source 10delivers to conduit 11, remote biogas source 12 delivers to conduit 13,remote biogas source 14 delivers to conduit 15, remote biogas source 16delivers to conduit 17, remote biogas source 18 delivers to conduit 18,and remote biogas source 20 delivers to conduit 21. Each of theseconduits in turn feed biogas to a conduit 30 that ultimately connects toa main feeder conduit (“header”) 32, which is a portion of the networkof conduits, and that delivers the accumulated biogas to the centralprocessing facility 40. Processed gas (methane of combustible purity)that exits the central processing facility 40 in conduit 34, iscompressed in a system compressor 36 either into a pipeline 33 fordelivery to a power plant 37 for combustion, or to storage 35, and/or totank cars 39 to deliver. The biomethane may also be routed to processingto CNG 42. Moreover, the biomethane may also be charged to a fuel cell44 for direct conversion to electricity.

The remote biogas sources may not be of uniform size and are generallynot producing biogas at the same rates. Accordingly, with biogasavailability being variable within the system, controls are needed sothat the system can operate continuously with reasonable predictabilityof biomethane supply capability, as far as possible based on theavailability and expected availability of biogas from the sources. Ofcourse, even if all biogas supply from the biogas sources were shut in,there is still an amount of biogas held up in the volume of theconduits, and in the volumes within the central processing facility thatcould be available to process biomethane. Depending upon the rate ofcompression of gas, this gas hold-up in the system represents a“time-lag” within the system that a controller can take into account.

In the exemplary, simplified overview illustration of FIG. 1, thecontroller 70 receives data from each of the remote biogas sourcesrelating to biogas available to enter the network of conduits. Ofcourse, in some systems not all biogas sources will have suchcapability, and at least some may lack the measuring instruments todetect and transmit data about biogas availability. In the illustratedexample, the central controller 70 receives input data about biogasavailability from detector/transmitters 71, 72, 73, 74, 75, 76, and 78(or from human input based on observations at these remote sources). Thecentral controller 70 is configured to process this data to control therate of gas compression at a biogas compressor at each remote source(not shown in FIG. 1; shown in FIG. 2 as compressor 220 at eachexemplary remote source), and control the biogas feed compressor (notshown in FIG. 1, but shown in FIG. 3 as compressor 45) at the treatmentfacility 40, as well as the biomethane gas compressor 36. By suitablycontrolling the rates of compression taking into account the volume ofpredicted available gas at each source, a predictable and relativelysteady rate of gas delivery can be achieved from the system to thenatural gas pipeline. Of course, if a portion of available biogas isbeing routed to a fuel cell at a remote source, the central controllerhas to take into account that this biogas is not available to thecentral biogas treatment facility.

Biomethane gas to the natural gas pipeline upgrader must be atacceptable purity and quality (H2S, O2, inerts, water, etc.). Theutility operator requires delivery into its point of interconnect (POI)at a flow rate between the minimum and the maximum rates as described inan interconnection agreement so that thee revenue metering equipment canremain within calibration. This min/max flow must be uniform and must becommunicated to the utility prior to delivery including a duration offlow.

FIG. 2 is another schematic simplified overview flow diagram, not toscale, of an example of a remote biogas source 200 that includes adigester 210 that produces biogas, and that has a flexible expandableroof 212, sealed in an airtight seal to the digester. Thus, producedbiogas 214 accumulates under the roof gradually causing the roof 212 toexpand upward from a first flat shape (shown in dark line), to anexpanded state billowed out upwards by biogas, as shown in dashed lines.An instrument, such as, but not limited to, a laser deflector measuringdevice 215 can be used to detect the degree of deflection of the roof212 and transmit this data to the central controller 70 (see also FIG.1). Based on this transmitted data, the central controller 70 cancontrol a rate of the local biogas compressor 220. The local compressor220 compresses biogas into the network conduit 30, as in FIG. 1, via aconnecting conduit 222. Network conduit 30 conveys the biogas to theconduit 32 that feeds biogas to the central processing facility 40. Asexplained with regard to FIG. 1, processed gas (biomethane) from thecentral processing facility 40 is charged to the system processed gascompressor 36, and thence to pipeline 33, under control of centralcontroller 70.

In an exemplary embodiment, the flow rate from the local biogascompressor 220 is measured by flow detector 224, which controls acontrol valve 226. This allows the recycling of a proportion of thebiogas back into the digester through valve 226, which can have thebenefit of reducing the hydrogen sulfide concentration in the biogas. Ingeneral, an amount of recycle of from about 2 to about 8 percent bymeasured volume of biogas can be helpful in this regard.

A hydrogen sulfide detector 230, or several of these, may be located inthe vicinity of the digester 210 and in the vicinity of the networkpipelines. When the detected level in the atmosphere increases above apreset threshold, the detector shuts down the cutoff valve 232 therebypreventing further flow of the gas through any leak that might havearisen. In addition, a signal may be sent to the central controller 70to indicate an alarm condition and initiate appropriate action.

FIG. 3 is a schematic overview of a flow diagram, not to scale,depicting process flows of an example of a central processing system 300that upgrades biogas to methane grade gas. Biogas from the plurality ofremote biogas sources enters the processing facility in conduit 32. Thisconduit feeds the raw incoming biogas to the hydrogen sulfide removalstage 310. In the exemplary embodiment, this includes a scrubber inwhich a solution of sodium hydroxide in water is contacted, preferablyin counter-current flow, with the raw biogas charged to the scrubber. Asillustrated in the example, sodium hydroxide solution 311 enters at thetop of the scrubber 310 flowing downward, while the biogas enters at thebase in 32 flowing upward. A portion of the sodium hydroxide solution isremoved from the bottom in conduit 313, a portion is recycled in conduit315, and the scrubbed biogas leaves the top of the scrubber in conduit312. After this scrubbing stage the hydrogen sulfide content of thebiogas is significantly reduced but might not yet meet combustionstandards.

For further biogas purification to meet combustion standards, the gas ischarged to an activated carbon gas purifying unit that removes residualhydrogen sulfide such that the purified biomethane meets standards forcombustion, as to residual hydrogen sulfide. As illustrated in theexample, a pair of activated carbon columns 321, 322 are used in tandemso that one is in use, while the other is being regenerated or refilled,as the activated carbon becomes spent. The packed columns may beequipped with sensors 323, 324 to detect hydrogen sulfide breakthroughin the packed beds to facilitate the switchover from one packed bed tothe other and maintain treated gas quality as the biogas exit in conduit314.

After the gas has been purified to remove hydrogen sulfide, the gas maycontain moisture. Thus, the purified biogas is now charged to a dryer330 where residual moisture is removed. Gas drying may be achieved witha desiccant packed into the dryer, or by other means. The dried gas inconduit 314 is charged to a carbon dioxide removal unit 340. Anon-limiting example of such a unit is a membrane gas separator, wherethe membrane is selected to separate the methane gas in the purifiedbiogas from the much larger carbon dioxide molecules also present inbiogas. The methane-rich gas exiting from this unit 340 in conduit 318has significantly reduced carbon dioxide content and is then routed to achiller 350 for cooling prior to controlled compression in the systembiomethane compressor 36 into a natural gas pipeline.

Summarizing, there is provided an exemplary method of aggregating andtreating biogas from a plurality of remote sources to convert the biogasto a processed combustible biomethane gas for compression to a naturalgas pipeline, or storage or processing to CNG or conversion toelectricity via a fuel cell. The method includes the steps of detectingthe availability of biogas at remote sources to permit prediction ofbiogas availability about 24-36 hours in advance, coupling the pluralityof remote biogas sources to a network of conduits and delivering thebiogas from the remote sources to a central processing facility.Treating the delivered gas by removing hydrogen sulfide in the biogas atthe central processing facility. The treatment may include contacting,in counter-current flow, with a solution of sodium hydroxide to reactwith the hydrogen sulfide. The method further includes removing traceresidual hydrogen sulfide and other contaminants by flowing the gasthrough activated carbon packed beds. The treated gas is charged to amembrane separator to separate out carbon dioxide from the desiredbiomethane in the biogas.

Other exemplary method steps may include measuring or observing adeflection of flexible roofs of remote sources and using the deflectionmeasurements or input observations via a central controller configuredto control the individual biogas compressors at the remote sources, thebiogas charge compressor at the central treatment facility and theprocessed gas compressor. Further, the methods may include measuringhydrogen sulfide concentration in the atmospheric environment at theremote biogas sources and along the network of conduits and using themeasured concentration to control cut-off valves when a predeterminedconcentration is detected indicating a leak.

The exemplary process flow diagrams of FIGS. 4 and 5 also illustratedetails of the processing of biogas from digesters, converting animalwaste to biogas, to biomethane (meeting combustibility specificationsset by regulations in the various states), and illustrate variationsfrom the foregoing examples of overview process flow diagrams. Ofcourse, the biogas may also be charged to fuel cells, as noted above, atthe remote sources or at the central location or anywhere in betweenwhere access to the biogas gathering/collection line is made available.And, the biomethane produced may also be used to manufacture CNG or toproduce electricity via fuel cells. Descriptions of certain ancillaryequipment previously discussed will not be repeated, but can be assumedto be present as appropriate. FIG. 4 illustrates an exemplary simplifiedbiogas conditioning process flow chart, and FIG. 5 illustrates anexemplary simplified process flowchart for conversion of biogas tobiomethane meeting regulatory standards for injection into a natural gaspipeline. In the exemplary embodiments, both FIGS. 4 and 5 illustratethe use of “skid-mounted apparatus.” Of course, other non-skid-mountedequipment might also be used.

As to FIG. 4, in the illustrated exemplary process flow diagram 400, theapparatus is located near the remote biogas source, such as on a dairyfarm, for example and are located on four skid platforms: 410, 440, 460and 480. In the first skid, the oxygen generator skid 410, air enters acompressor 412 and is charged to an oxygen generator unit 414. Thisoxygen, together with animal waste (manure in the case of a dairy farm)charged to a digester 416 where the waste is digested under conditionsthat generate methane gas—biogas. Biogas from the digester is drawnunder controlled conditions into the suction of a blower 420 and chargedto a condensate separator for removing condensate (water) carried in thebiogas. The condensate is recycled to the digester or to a sump 416. Thebiogas exits from the top of the separator 422 and is charged to theapparatus on skid 440 that perform the function of hydrogen sulfide(H₂S) removal from the biogas. In the illustrated example, the biogas ischarged first to an iron sponge 442 that removes a large proportion ofthe hydrogen sulfide. The removal process is monitored by H₂S gasanalyzers 443. The biogas then enters an activated carbon column 445where further amounts of H₂S are removed. The biogas exiting from theactivated carbon column 445 desirably has a level of H₂S concentrationthat is within limits regarded as safe for transportation in a pipeline.The cleaned biogas then enters the compressor system mounted to thecompressor skid 460. The biogas passes into a compressor suction gasscrubber 462 where water is removed and drained under control to therecycle water system conduit. The biogas is compressed in the compressor464, and the compressed biogas is cooled in the compressor cooler 466.The cooled, compressed biogas then flows through a compressor dischargescrubber for further moisture removal. The removed water is routed tothe water recycle conduit and the compressed biogas is charged to adehydration system mounted to skid 480. The compressed biogas enters afirst gas/gas pre-cooler heat exchanger 482 where cooled compressedbiogas is used to cool the incoming warmer compressed biogas. Thecompressed biogas is cooled to some extent in this pre-cooler thanenters into a water-cooled heat exchanger 484 where chilled water from awater chiller 486 further cools the biogas to the range of about 40° F.,for example. The chilled biogas then enters a chiller separator toremove any condensed water in the gas for recycle. The chilled biogasflows to the pre-cooler 482 to cool incoming biogas. Upon exiting fromthe pre-cooler, the now warmed biogas flows through a gas meter 490. Thebiogas is then either charged to a truck for transportation, or to apipeline to convey the biogas to a gas processing facility 500, asillustrated in exemplary form, in FIG. 5.

FIG. 5 illustrates an example of a process for treating biogas toconvert it to biomethane that meets regulatory standards for feeding thegas into natural gas pipelines for subsequent use in power generation,commercial use, and residential use. The process equipment may receiveincoming biogas from several biogas producing facilities, for examplelike that illustrated in FIG. 4. The process 500 shows apparatus mountedon four skids: 520, 540, 560 and 580. Biogas from a process such as thatillustrated in FIG. 4 enters a filter/separator 502, optionally mountedto skid 520. The liquid water separated from the biogas is routed inwater recycle conduit 530 for reuse. The filtered off gas is analyzed506, and the volume is measured 504 before being charged to a compressorsuction scrubber where water is removed from the biogas for recycling.The scrubbed biogas is compressed in the compressor 524, and thecompressed biogas is cooled in the compressor cooler 526. The exitingcooled compressed biogas enters a compressor discharge scrubber 528where condensate water is removed for recycling. The biogas flows to agas/gas precooler 542 on skid 540 where it is pre-cooled against colderbiogas, and thence to a chilled water cooler 544 where the biogas isfurther cooled. The cooled biogas is then charged to a chiller separator546 from which cold exiting biogas is routed to the pre-cooler 542 tocool the incoming biogas, and from which condensate water is routed torecycling. The cold biogas is analyzed 548 and routed to a pair oftandem operating activated carbon filter columns 550, 552 to removeresidual impurities in the biogas. The purified biogas exiting theactivated carbon treatment is analyzed 551 and charged to a series ofmembrane separators to remove carbon dioxide and thereby increase theconcentration of methane in the biogas. Carbon dioxide rich gas exitingfrom the membrane first stage 554 is analyzed 553, metered 557, andvented via a stack 563. Methane-rich biogas exiting the first stage 554is also analyzed 555 and flows into a second stage of membraneseparation 556. One portion of the exiting methane gas that includescarbon dioxide is routed to the blower 558 and recycled back to thecompressor suction scrubber 522 so that the biomethane in the gas streamis not lost but is recycled to be reprocessed and enriched in methanecontent. The other portion of the methane-rich biogas from the secondstage 556 is charged to the biomethane compression skid 560.

By recycling a selected appropriate portion of the methane-rich biogasfrom the second stage membrane 556, the concentration of methane in thesystem upstream from the membrane stages 554, 556 is increased and theconcentration in the gas exiting the membrane separation step isincreased. Clearly, the higher the proportion recycled, the higher themethane concentration at the exit of the separation stages 554, 556 willbe. Thus, the amount of recycle is set to a level that ensures theexiting biomethane for compression to the natural gas pipeline meetsspecifications.

Methane-rich biogas exiting the second stage separator 556 is analyzed561, and gas meeting methane specifications (hereafter biomethane) ischarged to a compressor system mounted on skid 560. The compressorsystem includes a compressor suction scrubber 562 to remove water fromthe biomethane and route the water to recycling. The biomethane is thencharged to compressor 564 and the exiting compressed biomethane iscooled in a compressor cooler 566. The cooled biomethane is charged to acompressor discharge scrubber to remove condensed water for recycling,and the biomethane is charged to a chiller skid 580 that includesfurther gas cooling apparatus. The biomethane enters a gas/gas precooler582 where it is cooled against chilled biomethane. Then, the pre-cooledbiomethane enters a water-cooled exchanger 584 where it is furthercooled (to around 40° F.) against cold water from water chiller 588. Anyseparated condensate is separated out in the chiller separator 586 androuted to recycle. The chilled biomethane is routed to the pre-cooler582 to cool incoming biomethane. The warmed biomethane then flowsthrough a gas analyzer 587 and a gas meter 589 and can then be routed at590 to a gas pipeline or other transport means. Gas analyzers and gasflow meters at each remote location measure and provide data to thecentral controller. The central controller receives as inputs variablesincluding but not limited to pressures, gas analyses, humidity, oxygen%, inert %, H2S ppm, data about the presence of other contaminants (e.g.siloxanes for waste water and landfills), and the like that are orbecome necessary under particular circumstances to control the entiresystem.

As pointed out here above, the treated biogas, now meeting natural gasspecifications, can be used in power plants as fuel, and can also beused as a substitute for fossil-fuel methane in production of CNG fortransport fuel. It can also be charged to fuel cells and converteddirectly to electricity. The overall effect of the systems proposedherein is to reduce greenhouse gas emissions.

The foregoing are descriptions of examples of the type of apparatus andthe nature of the process flows useful for systems for aggregating andprocessing of biogas to biomethane. While examples of embodiments of thetechnology have been presented and described in text, and some examples,by way of illustration, it will be appreciated that various changes andmodifications may be made in the described technology without departingfrom the scope of the inventions, which are set forth in, and onlylimited by, the scope of the appended patent claims, as properlyinterpreted and construed.

1. A biogas collection and purification system, the system aggregatingbiogas from a plurality of remote sources and treating the biogas toproduce biomethane, the system comprising: a network of conduitsconfigured to convey biogas from the plurality of remote sources of thebiogas based on a detected availability of biogas at the respectiveremote source; a biogas compressor located at each of the plurality ofremote sources, the biogas compressor controlledly supplying biogas to acollection header of the network of conduits; a central processingfacility receiving the biogas conveyed in the network of conduits fromthe plurality of sources of biogas via a feed biogas compressor of thecentral processing facility, the central processing facility processingthe biogas into biomethane, the central processing facility having: abiogas hydrogen sulfide removal stage; an activated carbon scrubber; acarbon dioxide removal stage; and a processed gas compressor configuredto compress the biomethane; wherein a central controller receives inputdata, including data about gas availability at the remote sources, andthe central controller controls the biogas compressors at each remotefacility the feed biogas compressor of the treatment facility, and theprocessed gas compressor.
 2. The system of claim 1, wherein the sourcesof biogas include organic animal waste anaerobic digesters.
 3. Thesystem of claim 1, wherein the source of biogas includes captured biogasfrom landfills.
 4. The system of claim 1, wherein at least some of theplurality of sources of biogas include fuel cells, and the fuel cellsconvert biogas directly to electricity.
 5. The system of claim 4,wherein the electricity is transmitted to a grid or used directly topower batteries of plug-in electrical vehicles.
 6. The system of claim1, wherein biomethane produced at the central treatment facility is usedto manufacture CNG.
 7. The system of claim 1, wherein biomethaneproduced at the central treatment facility is charged to a fuel cell todirectly produce electricity.
 8. The system of claim 1, wherein at leastsome of the sources of biogas includes a hydrogen sulfide sensor locatedto detect release of hydrogen sulfide into a surrounding vicinity of theat least some of the sources and control a valve based on the detection.9. The system of claim 8, wherein at least one of the sources of biogasincludes a flow sensor detecting a flow of biogas from the source, theflow sensor controlling a valve to recycle a portion of the flow back tothe at least one source of biogas.
 10. The system of claim 1, wherein atleast one of the plurality of biogas sources comprises: a flexible roof,the flexible roof expanding upward when an amount of generated biogasincreases and biogas pressure increases under the flexible roof; and alaser deflection measurement apparatus located and configured to measurea degree of deflection of the flexible roof as it expand upward underbiogas pressure, the laser deflection apparatus providing data to thecentral controller.
 11. The system of claim 1, wherein at least one ofthe plurality of biogas sources comprises: a digester having a flexibleroof, the flexible roof expanding upward when an amount of generatedbiogas increases and biogas pressure increases under the flexible roof;and wherein the flexible roofs are inspected at periodic intervals todetermine an availability of biogas at the respective digester of eachremote source, the biogas availability input as data to the centralcontroller.
 12. A biogas collection, purification and delivery systemcomprising: a plurality of remote sources of biogas from digesters oforganic animal waste, the plurality of biogas sources each having aflexible roof, and each configured either (a) with sensors to detect anavailability of biogas at the respective ones of the plurality of remotesources and transmitters to transmit data about availability to acontroller or (b) configured to permit an estimation of biogasavailability by human inspection; a biogas compressor at each of theplurality of remote sources configured to controlledly compress biogasinto a network of conduits configured to convey biogas from theplurality of sources of biogas; a central processing facilitycontrolledly receiving biogas via a biogas feed compressor from theplurality of sources of biogas and processing the biogas intobiomethane, the central processing facility having: a biogas hydrogensulfide removal stage; an activated carbon scrubber; a membrane-basedcarbon dioxide removal stage; and a biomethane gas configured tocontrolledly compress the biomethane; wherein the central controller isconfigured to control the biogas compressors at each of the plurality ofremote sources, to control the biogas feed compressor of the centralprocessing facility, and to control the biomethane gas compressor. 13.The system of claim 12, wherein at least one of the plurality of biogassources comprises: a flexible roof, the flexible roof expanding upwardwhen an amount of generated biogas increases and biogas pressureincreases under the flexible roof; and a laser deflection measurementapparatus located and configured to measure a degree of deflection ofthe flexible roof as it expands upward under biogas pressure, the laserdeflection apparatus providing data to the central controller aboutbiogas availability based on a degree of deflection of the flexibleroof.
 14. The system of claim 12, wherein at least one of the pluralityof biogas sources comprises: a digester having a flexible roof, theflexible roof expanding upward when an amount of generated biogasincreases and biogas pressure increases under the flexible roof; andwherein the flexible roofs are inspected at periodic intervals todetermine an availability of biogas at the respective digester of eachremote source, the biogas availability input as data to the centralcontroller.
 15. The system of claim 12, wherein at least one of theplurality of sources of biogas includes a hydrogen sulfide sensorlocated to detect release of hydrogen sulfide into a surroundingvicinity of the at least some of the sources, and control a valve. 16.The system of claim 12, wherein at least one of the plurality of sourcesof biogas includes a flow sensor detecting a flow of biogas from thesource, the flow sensor controlling a valve to recycle a portion of theflow back to the at least one source of biogas.
 17. The system of claim12, wherein the compressor is configured to compress methane derivedfrom processing of biogas in the central processing facility into anatural gas pipeline.
 18. The system of claim 12, wherein biomethaneproduced at the central treatment facility is charged to a fuel cell todirectly produce electricity
 19. The system of claim 18, wherein theelectricity is transmitted to a grid or used directly to power batteriesof plug-in electrical vehicles.
 19. The system of claim 12, whereinbiomethane produced at the central treatment facility is used tomanufacture CNG.
 21. The system of claim 12, wherein at least some ofthe plurality of sources of biogas include fuel cells, and the fuelcells convert biogas directly to electricity.
 22. The system of claim 4,wherein the electricity is transmitted to a grid or used directly topower batteries of plug-in electrical vehicles.
 23. A biogas collection,purification and delivery system comprising: a plurality of remotesources of biogas from digesters of organic animal waste, the pluralityof biogas sources each having a flexible roof, and each configuredeither (c) with sensors to detect an availability of biogas at therespective ones of the plurality of remote sources and transmitters totransmit data about availability to a controller or (d) configured topermit an estimation of biogas availability by human inspection; anetwork of conduits configured to convey biogas from the plurality ofremote sources of biogas; a central processing facility receiving biogasconveyed from the plurality of sources of biogas and processing thebiogas into combustible biomethane, the central processing facilityhaving: a biogas feed compressor controlledly charging biogas to thecentral processing facility; a biogas hydrogen sulfide removal stage; anactivated carbon scrubber; a carbon dioxide removal stage; and abiomethane compressor configured to compress the biomethane; wherein atleast some of the remote biogas sources include a fuel cell configuredto convert biogas directly to electricity; wherein a central controlleris configured to control the biogas compressors at each of the pluralityof remote sources, to control the biogas feed compressor of the centralprocessing facility, and to control the biomethane gas compressor, basedon data including biogas availability at respective ones of theplurality of remote sources.
 24. The system of claim 23, wherein atleast one of the plurality of biogas sources comprises: a flexible roof,the flexible roof expanding upward when an amount of generated biogasincreases and biogas pressure increases under the flexible roof; and alaser deflection measurement apparatus located and configured to measurea degree of deflection of the flexible roof as it expands upward underbiogas pressure, the laser deflection apparatus providing data to thecentral controller about biogas availability based on a degree ofdeflection of the flexible roof.
 25. The system of claim 24, wherein atleast one of the plurality of biogas sources comprises: a digesterhaving a flexible roof, the flexible roof expanding upward when anamount of generated biogas increases and biogas pressure increases underthe flexible roof; and wherein the flexible roofs are inspected atperiodic intervals to determine an availability of biogas at therespective digester of each remote source, the biogas availability inputas data to the central controller.
 26. The system of claim 23, whereinthe central controller controls the biomethane compressor is configuredto compress bio methane into a natural gas pipeline, based on data aboutbiogas availability at the plurality of remote sources predicted atleast 24 hours before.
 27. The system of claim 23, wherein biomethaneproduced at the central treatment facility is charged to a fuel cell todirectly produce electricity
 28. The system of claim 27, wherein theelectricity is transmitted to a grid or used directly to power batteriesof plug-in electrical vehicles.
 29. The system of claim 23, whereinbiomethane produced at the central treatment facility is used tomanufacture CNG.
 30. The system of claim 23, wherein electricity fromthe fuel cells is transmitted to a grid or used directly to powerbatteries of plug-in electrical vehicles.